Alzheimer's disease (AD) is characterized by extraneuronal plaques consisting of b-amyloid (A?) peptides and intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated, paired helical filaments of the microtubule-associated protein, tau. Multiple lines of evidence suggest that overproduction of A? in the brain is a major cause of AD, whereas hyperphosphorylated tau has been found in many neurodegenerative diseases known as tauopathies. Hence, identification of new genes/proteins involved in these processes is a major goal in AD research and may provide potential therapeutic targets. In the previous funding period, we applied the random homozygous gene perturbation (RHGP) technology to screen for genes involved in A? generation and identified a novel mouse gene, Rps23r1(previously named Fg01 in the original submission). Overexpression of the RPS23R1 protein can significantly reduce A? generation, tau phosphorylation and GSK-3 activity. Further in vitro studies showed that RPS23R1 interacts with adenylate cyclases, increasing cAMP synthesis, which upregulates PKA activity. Both activation of PKA and inactivation of GSK-3 are known to inhibit A? generation and GSK-3 inactivation also inhibits tau phosphorylation. The function of Rps23r1 was also demonstrated in transgenic mice expressing brain-specific Rps23r1. Furthermore, the AD-like pathologies of the APP/PS1/tau triple transgenic AD mice were ameliorated and levels of synaptic marker proteins were increased after crossing the mice with the Rps23r1 transgenic mice. Although Rps23r1 is a unique mouse gene, Rps23r1 produces the same phenotype in cells of various species including human. Rps23r1 originated through mouse Rps23 (ribosomal protein S23) mRNA retroposition, a process where mRNA is reintegrated into the genome resulting in gene duplication/evolution. Since Rps23 retroposition also occurred in humans, it is possible that humans possess functional Rps23r1 homologs. Our results suggest that RPS23R1- and functional human RPS23R1 homolog-mediated signaling pathways may play important roles in the pathogenesis of AD and other diseases, such as cancer and diabetes, in which PKA and GSK-3 are crucially involved. Therefore, in this competitive renewal proposal we aim to determine the functional domain(s) of RPS23R1, identify functional human Rps23r1 homologs, further characterize RPS23R1 and its human homologs and decipher mechanisms underlying their effects, specifically inhibition of A generation, tau phosphorylation and modulation of GSK-3 activity. We will cross brain-specific Rps23r1 transgenic mice with AD transgenic (Tg2576 and APP/PS1/tau triple) mice to determine whether Rps23r1 can ameliorate AD-like pathologies and behavioral/cognitive deficits. We will also generate Rps23r1 conditional knockout mice to explore other physiological functions of Rps23r1. The results of these studies are expected to provide important information for developing new strategies to combat AD and other diseases.